The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus such as copying machines, laser beam printers, printers and the like having a conveyance guide means for guiding a sheet material by one side reference. A description will be made with reference to the case of a copying machine.
Conventionally, sheet materials are conveyed by a method using one side of each sheet material as a reference or by a method using the central portion of each sheet material as a reference. However, due to the simple structure required for the apparatus, one side reference method is more often adopted, and therefore in the image forming apparatus a separation belt is used at only one side of the photosensitive drum.
In the conventional apparatuses when the original image is of A4 size, it is formed on a sheet material of A4 size, and when the original image is of B5 size, it is formed on a sheet material of B5 size. For this reason, irrespective of the method adopted for conveying sheet materials, no problem of image arrangement occurs in this case.
In an image forming apparatus the one side reference type adopting the sheet separation method by a separation belt, when an original image of A4 size is to be formed on a sheet material of A4 size, no problem of image arrangement occurs. However, when an original image of A4 size is to be formed on a sheet material of, e.g., B4 size, the reproduced image is deviated to one side of the sheet material, providing a poor image arrangement.